Old modem as a switch

This is my first year with multiple controllers. I will have 2 so I need a switch. Is it alright to use an old adsl modem as a switch or does being a modem somehow reduce it's capability as a switch. I've asked everyone I know if they have a spare switch. Figure I don't want to buy one if the old modem will do the job. Thanks.

I did once use an old modem as a switch and it worked fine for my purpose, just make sure to disable the DHCP server function and it should be good to go. Do remember to set a static IP address in the modem just in case you need to log back into it, that way you don't have to scan your network to find out what IP address it has.

The switch in a modem should be no different than a standard switch, and when our lighting equipment doesn't really utilize the full 100mb/s of the network anyway even if it was running a bit under powered it would still be able to put through enough data.

Go for it.
My show network is on an old ADSL modem. and that then feeds out to three unmanaged switches to in turn drive the elements in different areas of the house. And I can then use the WiFi part of the modem to connect back to the Pi that runs the show from a phone or tablet.

As kitman said, turn off DHCP or set your controller IPs in the range that is not used for DHCP. If it is a Telstra modem chances are it's IP is 10.0.0.138 and anything above .138 is not used for DHCP.